A Robust, Scalable Platform for the Electrochemical Conversion of CO₂ to Formate: Identifying Pathways to Higher Energy Efficiencies

Abstract

This work demonstrated a robust, scalable cell architecture for electroreduction of CO2 (CO2R). An up to 90% faradaic efficiency for the conversion of CO2R to formate at 500 mA/cm2 was realized at a 25 cm2 gas diffusion electrode (GDE) with a carbon-supported SnO2 electrocatalyst. A 1.27 mm thick catholyte was used between the bipolar membrane and cathode GDE, which could be further reduced to tens of micrometers upon refinement. The deconvolution of the potential drop from each individual component/process guides the pathways to higher energy efficiencies of CO2R at this platform. Significant changes in the agglomerate size and aspect ratio on the electrode before and after an 11 h test were revealed by nano-CT, suggesting reduced CO2 accessibility from electrode degradation. The versatility of this CO2R testing platform enables the ability to assess materials, components, and interactions at scales more in line with future devices.

Continuous Electrochemical Reduction of CO2 to Formate: Comparative Study of the Influence of the Electrode Configuration with Sn and Bi-Based Electrocatalysts

“…Finally, further research is still required to overcome current limitations and develop processes with performances that simultaneously optimize all the figures of merit analyzed in this study. In this regard, research efforts should focus on the development of new filter press configurations [ 70 , 71 ] such as the use of a three-compartment electrochemical reactor, bipolar membranes [ 72 ], or working electrode configurations [ 73 ] to enhance the mass transfer of the reagents and products in the counter and working electrode, and simultaneously address the synthesis of innovative electrocatalysts for both cathode [ 74 ] and anode [ 75 ] to reduce the energy consumption in both compartments of the electrochemical reactor.…”

Bioelectrochemical engineering analysis of formate-mediated microbial electrosynthesis

“…2). [21,23,37] We used experimental parameters describing electrochemical reduction towards HCOOand H2 on a Sn electrode because of its ability to selectively produce formate [18,53] and we compared operation with two different gas feed compositions: , 2 = 0.5, corresponding to an equal mixture of CO2 and O2 in the gas feed stream; and , 2 = 0.833, corresponding to a CO2 partial pressure of 1 atm for our model. Current density towards CO2 reduction or H2 production increases exponentially as a function of voltage following Butler-Volmer kinetics ( Fig.…”

“…higher salt and buffer concentrations, higher pHs that enable higher selectivity towards carbon products). [18,54,59] Issues associated with short-lived but toxic byproducts are lessened, [12,28] but simple strategies to directly integrate electrochemical and microbial media with minimal intermediate processing are still necessary. The two-reactor system does have some challenges, however, including increased gas and liquid pumping requirements and the increased number of failure or contamination points.…”

“…The choice of redox mediator requires careful consideration: the ideal one should be abundantly available or easily produced electrochemically (eliminating complex organic molecules and inorganic ions), electropositive enough to directly reduce NAD(P)H for efficient energy transfer to cellular metabolism, and highly soluble in liquid water (eliminating H2). [3,5] Formate/ic acid stands out as an especially promising redox mediator because it is readily and specifically produced from CO2 [18][19][20] and multiple natural and engineered formatotrophic growth mechanisms exist in workhorse bacteria. [21][22][23][24][25] Initial scale-up, [26] component integration, [27] and media optimization [28] studies have been performed for MES systems, demonstrating the need for careful attention to process parameters including the gas/liquid mass transfer coefficient (kLa).…”

A Comprehensive Modeling Analysis of Formate‐Mediated Microbial Electrosynthesis**

“…The choice of redox mediator requires careful consideration: the ideal one should be abundantly available or easily produced electrochemically (eliminating complex organic molecules and inorganic ions), electropositive enough to directly reduce NAD(P)H for efficient energy transfer to cellular metabolism, and highly soluble in liquid water (eliminating H 2 ) [3,5] . Formate/ic acid stands out as an especially promising redox mediator because it is readily and specifically produced from CO 2 [18–20] and multiple natural and engineered formatotrophic growth mechanisms exist in workhorse bacteria [21–25] …”